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61.
Summary A method was devised to assay four forms of vitamin C: L-ascorbic acid (AA), dehydroascorbic acid (DHA), ascorbate-2-mono-
and polyphosphate (AMP, APP), as well as ascorbate-2-monosulphate (AMS), in sample series of different fish tissues and feed.
Direct and indirect detection were combined. Sample extractions were carried out with 0.2 mol L−1 sodium acetate buffer (pH 4.8) and extracts were deproteinized after different chemical or enzymatic reactions, with perchloric
acid. The DHA was reduced to AA with dithioerythritol (DTE). Ascorbate oxidase enzyme was used for the detection of background
and an acidic phosphatase enzyme for the hydrolysis of different phosphate esters. Ascorbate-2-sulphate was detected directly
with help of coinjection of the compound. Chromatographic analysis was carried out with a single column isocratic reverse
phase method. The mobile phase was an aqueous buffer of 0.04 M sodium-acetate, 0.05 mM EDTA, 0.5 mM tetrabutylammonium dihydrogen
phosphate (TBA) adjusted to pH 3.76 with 85% H3PO4 and with 24 mL methanol added to 1000 mL. C-18 columns were used with 0.6 mL min−1 flow rate at 23°C. The vitamin C forms were detected by UV absorption at 250 nm. The determination limit was 1.0–5.0 μg g−1 in AA equivalent. The standard deviations were between 1–6% and depended on the concentrations of vitamin C forms and tissues.
Recoveries were between 90–96% in samples.
Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997 相似文献
62.
利用水热法和直接沉淀法, 设计合成了5例由过渡金属(TM)-联咪唑配阳离子与Dawson型钨磷酸阴离子构成的多金属氧酸盐(POM)基有机-无机杂化化合物[Ni(H2biim)3]4[Ni(H2biim)2(P2W18O62)2]·2H2O(1), [CoIII(H2biim)3]2[P2W18O62]·8H2O(2), [Cu(H2biim)2]3[P2W18O62]·4H2O(3), [CoII(H2biim)3]2H2[P2W18O62]·9H2O(4)和 [Ni(H2biim)3]3[P2W18O62]·2H2O(5); 并利用X射线单晶衍射分析(SC-XRD)、 红外光谱(IR)和热重-差热分析 (TG-DTA)等对其进行了表征. 化合物1~5作为载体用于固定辣根过氧化物酶(HRP)时, 显示出了较高的酶固定化能力. 另外, 利用圆二色光谱(CD)和激光扫描共聚焦显微镜(LSCM)等方法评价了固定化酶HRP/1~HRP/5的重复使用性、 储存稳定性和检测过氧化氢(H2O2)的性能. 由于该类POMs与HRP间存在强的相互作用, 利用简单的物理吸附法即可实现POMs对HRP的固载. POMs对酶的固定不但提高了HRP对使用及储存环境的耐受性, 同时也拓展了POMs在酶固定化领域的应用. 相似文献
63.
磁共振成像(MRI)是一种强大的非侵入式生物医学诊断技术. 临床上, MRI需要借助造影剂来提高成像质量, 从而提高诊断的准确性. 由于具有优越的信号放大能力和生物相容性, 自组装多肽探针可负载特定的MRI分子, 通过酶促自组装过程实现肿瘤靶向和特异性富集, 增强肿瘤病灶区MRI信号, 从而进一步提高MRI的准确性和灵敏度. 本综述总结了近年来多肽自组装探针在不同MRI模式( 1H MRI, 19F MRI和双自旋核MRI)下的最新进展, 并展望了这类新型探针在MRI领域的应用前景. 相似文献
64.
酶作为一种具有高度特异性和高效性的催化剂, 可在细胞器中通过复杂有序的生化反应调节细胞的代谢过程. 受细胞区隔化结构的启发, 仿生设计纳米酶催化体系、 构筑限域酶催化微环境从而提高酶催化活性的研究为酶催化应用开辟了新思路. 纳米催化体系保留了小尺寸、 大比表面积、 肿瘤部位选择性富集等优势, 在疾病的诊疗方面发挥了巨大的优势. 本文首先总结了天然酶、 模拟酶和级联酶体系的催化机理, 对仿生构筑的纳米酶催化材料的载体体系进行了概述, 介绍了纳米酶催化体系在生物成像方面的应用, 讨论了其在相关代谢类疾病的作用途径, 并对纳米酶催化体系用于生物诊疗的发展前景进行了展望. 相似文献
65.
Bulk-modified epoxy-graphite tyrosinase biosensors were fabricated by four different procedures. The influence of these fabrication procedures on the analytical performance of the enzyme electrode in an amperometric wall-jet flow cell has been studied. The bioprobe performance is assessed by cyclic voltammetry. Higher current densities and narrower peaks were obtained when the enzyme was introduced in the dry state into the epoxy-graphite material, instead of introducing it previously dissolved in the buffer. In the F1 system responses of 11.79 μA cm−2 and 1.43 μA cm−2 are then obtained for catechol and phenol respectively for 50 μL injections of 20 μM solutions. Moreover, if gold/palladium is introduced into the epoxy-graphite, a further increase in current is achieved resulting in 27.70μA cm−2 and 4.90μA cm−2for catechol and phenol, respectively. This biosensor can operate in aqueous as well as in mixed aqueous-organic environments. 相似文献
66.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(26):7723-7727
The Friedel–Crafts acylation is commonly used for the synthesis of aryl ketones, and a biocatalytic version, which may benefit from the chemo‐ and regioselectivity of enzymes, has not yet been introduced. Described here is a bacterial acyltransferase which can catalyze Friedel–Crafts C‐acylation of phenolic substrates in buffer without the need of CoA‐activated reagents. Conversions reach up to >99 %, and various C‐ or O‐acyl donors, such as DAPG or isopropenyl acetate, are accepted by this enzyme. Furthermore the enzyme enables a Fries rearrangement‐like reaction of resorcinol derivatives. These findings open an avenue for the development of alternative and selective C−C bond formation methods. 相似文献
67.
68.
A microtiter plate assay for quantitation of reduced (GSH) and oxidized (GSSG) glutathione in the rat liver tissue and bile
is described. The assay is based on the established enzymatic recycling method and a new thiol-masking reagent, 1-methyl-4-vinyl-pyridinium
trifluoromethane sulfonate (M4VP). Samples were first processed by homogenization with (liver) or addition of (bile) sulfosalicylic
acid. The total glutathione and GSSG were then determined before and after rapid (≤2 min) and efficient (100%) masking of
the GSH content of the samples with M4VP followed by the enzymatic recycling assay. The percentages of error and coefficient
of variation of the assay were within the accepted guidelines, indicating the accuracy and precision of the assay in the range
of 6.25–100 pmol GSH per microplate well and 2.17–140 pmol GSSG per well, with lower limit of quantitation of 6.25 and 2.17 pmol
per well for GSH and GSSG, respectively. Furthermore, the recoveries of added GSH or GSSG from the liver and bile samples
were accurate and precise. The assay was applied to measurement of GSH, GSSG, and GSH:GSSG ratio in the liver and serially
collected bile samples in sham-operated and ischemic rat livers, demonstrating a depletion of glutathione and a decrease in
the GSH:GSSG ratio as a result of ischemia. The developed assay is rapid, sensitive, accurate, and precise and is suitable
for studies of the redox status of liver under physiologic and pathophysiologic conditions. 相似文献
69.
In developing new insulin-mimetic zinc(II) complexes with various ligands including a biodegradable polymer, we prepared and characterized a Zn(gamma-pga) complex in solution as well as in solid, and investigated its in vitro insulin-mimetic activity and in vivo antidiabetic effect in type-2 diabetic KKA(y) mice. The in vitro insulin-mimetic activity of the Zn(gamma-pga) complex was considerable better than that of ZnSO(4). The Zn(gamma-pga) complex normalized the hyperglycemia in KKA(y) mice within 21 d when administrated orally at doses of 10-20 mg (0.15-0.31 mmol) Zn per kg body mass for 30 d. In addition, the impaired glucose tolerance, elevated HbA(1c) levels and metabolic syndromes were significantly improved in Zn(gamma-pga)-treated KKA(y) mice relative to those administrated with saline and ZnSO(4). 相似文献
70.
Beatrice Battistella Dr. Thomas Lohmiller Dr. Beatrice Cula Prof. Dr. Peter Hildebrandt Dr. Uwe Kuhlmann Prof. Dr. Holger Dau Dr. Stefan Mebs Prof. Dr. Kallol Ray 《Angewandte Chemie (International ed. in English)》2023,62(12):e202217076
In class Ib ribonucleotide reductases (RNRs) a dimanganese(II) cluster activates superoxide (O2⋅−) rather than dioxygen (O2), to access a high valent MnIII−O2−MnIV species, responsible for the oxidation of tyrosine to tyrosyl radical. In a biomimetic approach, we report the synthesis of a thiolate-bound dimanganese complex [MnII2(BPMT)(OAc)2](ClO)4 (BPMT=(2,6-bis{[bis(2-pyridylmethyl)amino]methyl}-4-methylthiophenolate) ( 1 ) and its reaction with O2⋅− to form a [(BPMT)MnO2Mn]2+ complex 2 . Resonance Raman investigation revealed the presence of an O−O bond in 2 , while EPR analysis displayed a 16-line St=1/2 signal at g=2 typically associated with a MnIIIMnIV core, as detected in class Ib RNRs. Unlike all other previously reported Mn−O2−Mn complexes, generated by O2⋅− activation at Mn2 centers, 2 proved to be a capable electrophilic oxidant in aldehyde deformylation and phenol oxidation reactions, rendering it one of the best structural and functional models for class Ib RNRs. 相似文献